I am nothing if not self-critical. And so a partial retraction may be in order.  In A Problem for Hylomorphic Dualism in the Philosophy of Mind, I opened with:

1) A primary substance (a substance hereafter) is a concrete individual.  A man, a horse, a tree, a statue are stock examples of substances.  A substance in this technical sense is not to be confused with stuff or material. Substances are individuals in that they have properties but are not themselves properties.  Properties are predicable; substances are not. Substances are concrete in that they are causally active/passive. 

What I wrote is not obviously wrong as a summary of what Aristotle means by ‘primary substance,’ (πρότη οὐσία) and I could cite  Aristotle commentators who have maintained something similar. But it is not obviously right either. Although it comports well with what we find in the Categories, it does not agree with what we read in the later Metaphysics, and in particular, Metaphysics VII (Zeta).  For in the latter work, Aristotle maintains the surprising thesis that each primary substance is identical with its essence. (VII.6) This is what Aristotle seems to be saying at 1031b18-20 and at 1034a4-6 in Metaphysics Z.  In the first of these passages we find, “each thing-itself [auto hekaston] and its essence are one and the same . . . .” In the latter place, we read, “in the case of things that are said in respect of themselves and  primary, X and the essence of X are the same and one . . . .” (Montgomery Furth tr.)

Why is this surprising?

Well, if following the Categories we take Socrates to be a clear example of a primary substance, and if a primary substance is identical to its essence (substantial form), then it is difficult to see how Socrates could be a hylomorphic compound, which he surely is, if not according to the Categories, then according to the Metaphysics.  After all, a composite composed of two complementary but non-identical elements cannot be identical to either. The following is quite obviously an inconsistent triad:

1) Socrates is a matter-form composite, a hylomorphic compound, a unity of two complementary but non-identical ‘principles’ (archai) or ontological factors, matter and form, neither of which can exist actually (as opposed to potentially) without the other.  That is: no actual parcel of matter can exist without having some substantial form or other, and (contra Plato), no substantial form of a material thing can exist without material embodiment.

2) Socrates is a primary substance.

3) Every primary substance is identical to a substantial form (essence, eidos).

These propositions are collectively inconsistent: any two of them, taken in conjunction, entails the negation of the remaining one. The triad above is known in the trade as an antilogism, and to each antilogism, there are three corresponding valid syllogisms.  

Syllogism A is an argument from (1) and (2) to the negation of (3).  Syllogism B is an argument from (2) and (3) to the negation of (1). Syllogism C is an argument from (3) and (1) to the negation of (2).  Each of these syllogisms is valid, but only one is sound.  Which one? That is the problem.

The problem can also be framed as follows. The limbs of the antilogism cannot all be true. So which limb of the antilogism (inconsistent triad)  should we reject?  Aristotle cannot abandon (1), for that would be to abandon hylomorphism. And he cannot abandon (3) given the textual evidence cited above.  So it seems that (2) has to go. Or rather, (2) has to go if we assume that the Metaphysics is an advance over the Categories and represents Aristotle’s mature position.

The rejection of (2), however, would appear to send us from the frying pan into the fire. If Socrates is not a primary substance, what would be? But before explaining this incendiary transition, let us first try to understand what motivates Aristotle’s surprising identification of primary substances with substantial forms at Metaphysics VII.6.

Why does Aristotle identify primary substances with substantial forms?

We begin by reminding ourselves that Aristotle’s inquiry into primary substance is a quest for the ultimately real, the ontologically basic, that upon which the reality of everything else depends. For Aristotle, ontology is ousiology, the search for the primary ousiai or substances or primary beings.  He never doubts that there are primary beings (basic entities or basic existents) upon which all else is ontologically dependent. And so he never countenances the possibility that the solution to any of the aporiai he sets forth could be solved by denying either the existence of substances or their plurality.  Being is many, not one, and the many beings are fundamentally real in that they are the supports of their properties and remain self-same over time.  In contemporary analytic jargon they persist by enduring not by perduring.

That there is a real plurality of primary substances is thus a fundamental presupposition of Aristotle’s ousiological ontology. The  existence of primary substances/beings, as a presupposition of ontological inquiry, is thus not a matter for inquiry. What is a matter for inquiry is the question: Which items are the items that satisfy the requirements of primary substance? That there are primary substances the Stagirite takes for granted; what they are is up for grabs.* Hence it cannot be simply assumed that concrete individuals such as a man, a horse, a tree, or a statue are primary substances despite the intuitive appeal of this notion and the support it finds in the Categories.  This is something to be investigated. 

Now there are  three main candidates for the office of primary substance. The three candidates are matter, form, and the hylomorphic compound, the composite of matter and form.

So either Socrates, who stands in here for any primary substance, is identical to matter, or he is identical to form, or he is identical to a matter-form (hylomorphic) composite.  Now he can’t be identical to matter as  Jonathan Lear explains:

. . . matter cannot be primary substance, for it is not something definite, nor is it intelligible, nor is it ontologically independent. As Aristotle puts it, matter is not a ‘this something.’ [tode ti] His point is not that matter is not a particular, but that matter is not an ontologically definite, independent entity. (Aristotle: The Desire to Understand, Cambridge UP, 1988, 271)

That sounds right. Primary substances are ontologically basic existents upon which all else depends for its being. An ontologically basic existent must be something definite (horismenos) that is both intelligible (understandable) and ontologically independent (choristos).  A smile, for example, is intelligible, and it is definite, but is not ontologically independent and thus not a substance. A smile cannot exist in itself, but only in another, namely, in a face.  You could say that the being of a smile is parasitic upon the being of a face.  You can have a face without a smile, but not a smile without a face. 

Lear is arguing on Aristotle’s behalf:  (i) Primary substances must be ontologically independent and definite; (ii) matter is neither ontologically independent nor definite; ergo, (iii) matter is not primary substance. So far, so good.  

You might object that the matter of Socrates and the matter of Plato are definite. But what defines or delimits these parcels of matter are Socrates and Plato, respectively, or rather what I will call their ‘wide essences’ or ‘wide quiddities’ by which I mean the conjunction of essential and accidental determinations appertinent to each: these parcels are  two because Socrates and Plato are two, and not the other way around.  

Lear, then, is right: matter cannot be primary substance.

Surprisingly, however, Socrates cannot be identical to a hylomorphic composite either. For “a composite is ontologically posterior to its form and matter.” (Lear, 277) Nothing counts as a primary substance, however, unless it is ontologically prior to everything else.  Thus Lear is arguing:

4) Nothing is a primary substance unless it is ontologically independent, ‘separate’ (choristos).

5) Every hylomorphic compound or material composite is ontologically posterior to, and thus ontologically dependent on, its components, matter and form. 

Therefore

6) No hylomorphic composite is a primary substance.

There is no way around this argument, as far as I can see. Therefore, of the three candidates, matter, form, and the hylomorphic compound, Aristotle concludes that substantial form is primary substance. (Note that accidental forms such as Socrates’s snubnosedness cannot be primary substance because of their lack of ontological independence.) But what is substantial form? Substantial form is essence where essence is ‘the what it is’ (to ti esti, τὸτί ἐστι)  of the thing, a calque of which is the Latin quidditas, whatness, quiddity.

Aristotle’s conclusion, then, in Metaphysics Zeta, is that, “each primary substance is identical with its essence.” (Lear, 279) Essence is what the mind comprehends, or at least apprehends. Essences are made for the mind, and the mind for essences. In this way the intelligibility requirement is satisfied. Matter as such is unintelligible, and hylomorphic compounds are intelligible only in their formal aspects.   Essences are the ontological correlates of definitions. A good definition ‘captures’ an essence in words. Thus ‘Man is a rational animal,’ while defining the term ‘man,’ points the mind beyond the word on the linguistic plane to to the essence on the ontological plane. These last sentences are my gloss on Lear’s gloss on Aristotle.

From the Frying Pan into the Fire

Aristotle is telling us that Socrates is identical to his essence or substantial form. This identification satisfies the  intelligibility requirement. Recall, however, that there are two requirements that need to be satisfied for anything to count as a primary being or basic entity.  Intelligibility is not enough. The other is that the item must be ontologically independent (choristos).  But independent is precisely what Aristotelian forms are not. For Plato, forms are ontologically independent of the phenomenal particulars that may or may not embody them here below. Plato’s Forms exist whether or not they are embodied or exemplified.  Not so for Aristotle who, figuratively speaking, brings the forms from their heavenly place (topos ouranios) down to earth. An Aristotelian substantial form of a material thing cannot exist without being embodied, ‘enmattered.’ On a hylomorphic assay of concrete individuals (a rock, a tree, a cat, a man, a statue), matter and form are  two complementary but non-identical components neither of which can exist without the other.

Aristotle appears to have painted himself into a corner.  He assumes, reasonably enough given what our outer senses reveal, that the world we encounter consists of a plurality of basic entities or primary substances.  

Relatedly, how is it logically possible for all of the following propositions to be true given what Aristotle appears to be maintaining in Metaphysics Z?

4) Socrates and Plato are numerically different human primary substances.

2) A primary substance is (identically) an essence or substantial form.

5) Socrates and Plato have the same substantial form or essence, where the essence is the ontological correlate of the  definiens of the definition that applies to them both univocally, namely, ‘A human being is a rational animal.’

I’ll end with a suggestion: Platonism lives on in Aristotle inasmuch as the substantial form is the primary substance, and not the concrete material particular.  The difference between the two titans of Greek philosophy is less than you thought. It is sometimes said that every philosopher is either a Platonist or an Aristotelian. My suggestion implies that this is not so. It is rather that every philosopher qua philosopher, if he is the real deal, is a Platonist. Plato dominates his best student. If so, A. N. Whitehead vindicatus est:  all of philosophy is but a series of footnotes to Plato, the ‘divine’ Plato as I sometimes call him.  Or as our very own Ralph Waldo Emerson once said, “Plato is philosophy and philosophy Plato.”

My claim about the dominance of Plato is obviously tendentious.  But if a man cannot be tendentious in the pages of his own weblog, where can he be tendentious?

For commentary on Raphael’s painting see my Substack entry, A Battle of Titans.

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*Aristotle takes it for granted that there is a plurality of primary substances. Is that self-evident? Put the question to Spinoza, and he would say that there is exactly one primary substance, deus sive natura, and that what Aristotle takes to be primary substances are mere modes of God or nature.   What would Plato say? Well he certainly would not say that Socrates and his toga are primary substances; they are merely phenomenal particulars, and insofar forth insubstantial, a blend of being and nonbeing.  He would give the palm to the eide, which are many, and beyond them to the Good, which is one.

Aristotle also takes it for granted that there are primary substances. Is that self-evident? Not to the exponents of the Madhyamika system. See T. R. V. Murti, The Central Philosophy of Buddhism.